Was this very early this morning, around 12am-1am 11th Dec? I noticed they (the HD versions of One, TV2 and TV3) were out around then. But as I had just changed LNBs last night I thought my alignment may have been off. Thought it was wierd though as I had adjusted for great signal and all other channels were working.
Since you noticed the same thing around the same time my guess is something was up with that transponder (12358 MHz)... maybe Sky were fiddling with the signal!
I had the atmoshpheric condition mesage on every channel around that time and an extra red light on the machine itself. Was fine when I checked before work this morning. Oddly, the programme I was recording from 11.30-12.30 seems to have recorded perfectly despite apparently having no signal when it was on.